I first came across this problem in the mid 1990’s when someone gave me a bottle of Slovenian white wine which must have spent a few days on a frozen lorry travelling across Europe to get to the UK. Tiny crystals of Potassium bitartrate had formed in the bottom of the bottle. It didn’t affect the taste it just made the last drop a bit crunchy!
Don’t be offended if you find crystals in a still white or rose wine, it is not a fault per se, and it might even show that the wine was made in a more “natural” way. Crystals also do not impact on the organoleptic qualities of the wine: they are just tartrates.
However, at Rathfinny we are talking about sparkling wine. The presence of crystals in a bottle of sparkling wine is pretty much a disaster.
Combine dissolved CO2 and tartrate crystals and you have a gushing wine fountain, not as spectacular as what one can see at the Formula 1 podium, but sometimes such bottles can lose half of their contents.
[My wife, Sarah, says unless you’re a chemistry bore – stop reading now!]
Tartaric acid is naturally present in grapes. So is Potassium. Both can combine, and while the resulting salt is soluble in grape juice or ‘must’, it becomes insoluble when alcohol is present, and crystals will form at lower temperatures.
What the winemaker will normally do to protect the wine is called “cold stabilization”: different techniques can be used that ensure these crystals will not develop in the wine after it is in the bottle.
The most normal method adopted is to cool the wine down to -4Celcius for a number of days or weeks in order for the crystals to form and drop out of the wine. The wine can then be bottled and is deemed to be “cold stabile”. However, this requires huge amounts of electricity to reduce the temperature of the tanks of wine to the required temperature and keep it at that temperature for the required length of time. Another method, which we are considering is ‘electrodialysis’.
Sounds high tech? A little bit: Electrodialysis is a technique of separation through membranes of positively charged elements (cations) and negatively charged elements (anions) under electric current. Membranes will let through either cations or anions. It will remove principally tartaric acid, charged negatively, and Potassium, charged positively.
The whole process is automatic; there is a simple test that has to be done for each wine to determine how the unit is going to run, since each batch of wine is different and unique in its composition.
Why would one choose electrodialysis over more classic cold stabilization techniques?
Well, each technique has pros and cons. For example, the technique using cold temperatures to bring the wine below freezing temperature, will initiate crystallisation in a tank. The crystals will be sticking to the wall and to the bottom of the tank, then the wine will be gently transferred into another tank, without crystals. Cream of tartar (basically, crystals of potassium bitartrate) can be added to the wine to enhance and speed up crystallisation. And as stated earlier this technique is highly demanding in energy and requires lots of cleaning of tanks!
On the other hand Electrodialysis can run continuously, does not require a lot of energy, is safe, precise, does not affect the wine’s qualities, does not require additives of any sort… it requires some chemicals, and some water. All effluents will go directly into our wastewater treatment plant.
We are still investigating if this is something we want, but it looks like it might be a pretty good option for us down the line.